X-2 Technical Service Manual Adjustments 7-13
Publication No: 15-02047
7.12 Receiver Performance Checks
7.12.1 Sensitivity and S+N/N ratio
Connect an AC Voltmeter across the audio output. Set the Signal Generator
frequency 1 kHz above the SCF of the selected channel (1 kHz below for
LSB) and connect the output, set to 0.4 µV PD, to the selected Antenna
socket. Adjust the volume control for a suitable near full scale dB reading on
the AC Voltmeter. Take note of the reading.
Switch off or adjust the Signal Generator output to a frequency outside the
receiver passband and check that the audio output drops by at least 10 dB.
7.12.2 AGC Check
Set up as for the Sensitivity test (refer to Section 7.12.1) but with the Signal
Generator output set to 50 mV PD. Adjust the volume control for a suitable
near full scale dB reading on the AC Voltmeter. Take note of the reading.
Reduce the Signal Generator output until the receiver output drops by 6 dB.
The Signal Generator level should be less than 2.5 µV PD.
7.12.3 Audio Output
Set up as for the Sensitivity test (refer to Section 7.12.1) but with the Signal
Generator output set to 50 µV PD. Connect an Oscilloscope in parallel to
the AC Voltmeter across the audio output.
Increase the Volume control and check the audio output exceeds 4 V RMS
at the onset of clipping displayed on the Oscilloscope.
Note: For this test it is permissible to replace the loudspeaker with a 5 W
8 Ω resistor.
7.12.4 Selectivity (USB operation)
Set up as for the Sensitivity test (refer to Section 7.12.1) but with the Signal
Generator output set to 0.5 µv PD and note the audio output reference level
on the AC meter.
With a Frequency Counter monitoring the Signal Generator, adjust the
frequency to -1 kHz and then to +4 kHz from SCF. Increase the Signal
Generator to 0.5 mV PD (+60 dB above 0.5 µV) and check the audio output
is less than the reference level at both frequencies.
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